CODEWITHSUNDEEP
iosobjective-ccore-image
Uttam
Uttam

Reputation: 236

how to find particular color in an uiimage and change that color

I want to find particular colour in an image,for example I have an image which has many colours.by assigning red parameter i want change other colour pixels except red colour pixels. please watch the below image. in the above updated image only blur colour is highlighted all other colours were changed.

enter image description here Updated Pic

enter image description here

Upvotes: 1

Views: 1032

Answers (1)

Losiowaty
Losiowaty

Reputation: 8006

Ok, so I got curious on how hard would it be to achieve this reverse chroma-key, and it turns out that given the example from Apple it is quite easy!

// Allocate memory
const unsigned int size = 32;
float *cubeData = (float *)malloc (size * size * size * sizeof (float) * 4);
float rgb[3], *c = cubeData;
CGFloat hue = CGFLOAT_MAX;

CGFloat minHueAngle = 210;
CGFloat maxHueAngle = 240;

// Populate cube with a simple gradient going from 0 to 1
for (int z = 0; z < size; z++){
    rgb[2] = ((double)z)/(size-1); // Blue value
    for (int y = 0; y < size; y++){
        rgb[1] = ((double)y)/(size-1); // Green value
        for (int x = 0; x < size; x ++){
            rgb[0] = ((double)x)/(size-1); // Red value
            // Convert RGB to HSV
            // You can find publicly available rgbToHSV functions on the Internet
            UIColor *color = [UIColor colorWithRed:rgb[0] green:rgb[1] blue:rgb[2] alpha:1];
            [color getHue:&hue saturation:nil brightness:nil alpha:nil];
            hue *= 360;

            // Use the hue value to determine which to make transparent
            // The minimum and maximum hue angle depends on
            // the color you want to remove
            float alpha = (hue > minHueAngle && hue < maxHueAngle) ? 1.0f: 0.0f;
            // Calculate premultiplied alpha values for the cube
            c[0] = rgb[0] * alpha;
            c[1] = rgb[1] * alpha;
            c[2] = rgb[2] * alpha;
            c[3] = alpha;
            c += 4; // advance our pointer into memory for the next color value
        }
    }
}
// Create memory with the cube data
NSData *data = [NSData dataWithBytesNoCopy:cubeData
                                    length:(size * size * size * sizeof (float) * 4)
                              freeWhenDone:YES];
CIFilter *colorCube = [CIFilter filterWithName:@"CIColorCube"];
[colorCube setValue:@(size) forKey:@"inputCubeDimension"];
[colorCube setValue:data forKey:@"inputCubeData"];

UIImage *originalImage = [UIImage imageNamed:@"yourImageName"];
CIImage *ciImage = [CIImage imageWithCGImage:originalImage.CGImage];
[colorCube setValue:ciImage forKey:kCIInputImageKey];


UIImage *result = [UIImage imageWithCIImage:[colorCube outputImage]];

This resulted in this image, from your example image : enter image description here

I've got to say it looks pretty decent, given I only tinkered with the values for a minute or two. Of course, to achieve the total end result you want, you'd need to use two more filters - namely CIPhotoEffectMono and CISourceOverCompositing to first make your original image black & white and then overlay the result from CubeMap filter on the black & white image.

Upvotes: 3

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